Power Electronics Question and Answers – Diode Circuits-1

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “Diodes Circuits- 1”.

1. An ideal diode has _________ &__________
a) some forward voltage drop, some reverse recovery time
b) high switching losses, high reverse voltage drop
c) no forward voltage drop, negligible reverse recovery time
d) no reverse recovery time, high leakage current
View Answer

Answer: c
Explanation: An ideal diode has no losses and negligible reverse recovery time.

2. A diode circuit is so arranged that when the switch is open it’s KVL gives
Ri+ 1/C ∫i dt = 0
When the switch is closed,
Ri+ 1/C ∫i dt = Vs
Vs is the dc supply voltage.
The diode is so connected that it is forward biased when switch is closed
The circuit is mostly likely be a
a) diode in parallel with Vs, switch, R & C
b) diode in series with R, than parallel with Vs & C
c) diode in series with the switch, R, C & Vs
d) diode in series with R,C & Vs with the switch connected in parallel across Vs
View Answer

Answer: c
Explanation: Examine the equation, the same current flows through R & C. Also when switch is open, the equation R.H.S is 0. Hence, all the elements are in series.

3. A circuit is so formed such that the source-R-C-diode-switch are in series. Consider the initial voltage across the C to be zero. The diode is so connected that it is forward biased when the switch is closed. When the switch is closed,
a) the current will decay exponentially & the voltage will increase exponentially
b) the current will increase exponentially & the voltage will increase exponentially
c) the current will fall to zero & the voltage both will decay exponentially
d) the voltage and current both remain constant
View Answer

Answer: a
Explanation: Instant switch is closed, the current is maximum Vs/R than starts to reduce, whereas voltage starts to increase from 0 to Vs (Capacitor Charging).
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4. The time constant of a series RC circuit (τ) is given by
a) R/C
b) C/R
c) RC
d) 1/RC
View Answer

Answer: c
Explanation: For a series RC circuit, τ = RC.

5. A circuit is so formed such that source-R-L-diode-switch are all in series. Consider the initial current in L to be zero. The diode is so connected that it is forward biased when switch is closed.
When the switch is closed,
a) the current will decay exponentially & the voltage will increase exponentially
b) the current will increase exponentially & the voltage will decay exponentially
c) the current will fall to zero & the voltage both will decay exponentially
d) the voltage and the current both remain constant
View Answer

Answer: b
Explanation: Instant switch is closed, the current is minimum zero than starts to increase till it reaches a constant value Vs/R, whereas voltage starts to reduce from Vs to 0 (Inductor Charging).

6. In the figure shown below,
The voltage across the diode decreases to zero as the switch is pressed
As the switch (shown in the green) is pressed, the voltage across the diode(ideally)
a) increases to Vs/R
b) increases to Vs
c) decreases to zero
d) remains Constant
View Answer

Answer: c
Explanation: As the switch is pressed, current starts to flow & the whole supply voltage (ideally) appears across the load R & voltage across the diode is zero.

7. For a diode circuit the voltage across the capacitor is given by
Vc(t)= Vs(1-e(-t/RC))
Then the initial rate of change of capacitor voltage is given by
a) 0
b) ∞
c) Vs x RC
d) Vs/RC
View Answer

Answer: d
Explanation: Find d(Vc)/dt and put t = 0.
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8. In the circuit show below,
The current through the inductor increases from zero to Vs/R
The initial current through the inductor is zero. When the switch (shown in green) is closed, then the current through the inductor
a) decreases from Vs/R to 0
b) increases from zero to Vs/R
c) decreases from Vs/L to 0
d) increases from zero to Vs/L
View Answer

Answer: b
Explanation: Current increases from zero to maximum value gradually due to the L nature. The KVL when switch is closed gives,
Ri + Ldi/dt = Vs
Solve for i(t). Maximum value comes out to be Vs/R.

9. In the figure shown below,
The voltage across the diode decreases to zero as the switch is pressed
When the switch is open, the voltage across the diode (ideally)
a) is Vs/R
b) is Vs
c) is zero
d) none of the mentioned
View Answer

Answer: b
Explanation: When the switch is open, the diode experiences all the supply voltage.
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10. The time constant of a series RL circuit (τ) is given by
a) R/L
b) L/R
c) RC
d) 1/RL
View Answer

Answer: a
Explanation: The time constant τ for a series RL circuit is R/L.

Sanfoundry Global Education & Learning Series – Power Electronics.

To practice all areas of Power Electronics, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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